This invention relates to a valve drive mechanism for a four-stroke cycle engine and more particularly to an arrangement for more fully controlling the valve operation over wide ranges of engine running conditions.
It is well understood that the opening and closing of the intake and exhaust valves of a four-cycle engine is particularly important in determining the engine performance. Conventional valve timing mechanisms have provided fixed lift curves and fixed duration for the individual valve operation. As a result, the valve timing and lift curve have been a compromise in order to provide good performance over a wide a range as possible.
In order to further improve the performance of an engine, it has been proposed to employ a variable valve timing mechanism which can be utilized to shift the phase of the valve opening and closing to vary overlap between the opening of the intake and exhaust valves under some running conditions to improve performance. Under other running conditions, the overlap is eliminated in order to improve running under those other conditions.
It is has also been recognized that there are advantages in changes the actual lift of the valve and the actual shape of the lift curve. This has generally been accomplished by using a plurality of cam lobes for operating an individual valve with varying types of mechanisms for determining which cam lobe operates the valve at a given running condition.
It has also been proposed to utilize both the variable valve timing and variable valve lift mechanisms in the same engine. However, this combination provides a very complicated structure and generally requires a number of cams, followers and a hydraulic mechanism for varying the valve timing and lift. In addition, these mechanisms do not make is possible to obtain continuously variable timing and lift for the most part.
It is, therefore, a principal object to this invention to provide an improved valve operating mechanism for a four cycle engine wherein both the lift curves and timing curves can be adjusted by simple mechanisms that do not require expensive or complicated controls or hydraulic circuitry.
It is a further object to this invention to provide a variable valve lift and timing mechanism for an engine wherein both lift and the timing curve can be adjusted without utilizing complicated structures and multiple lobe camshafts and followers.
It is a still further object to this invention to provide an improved and simplified valve operating mechanism for a four cycle engine that provides a wide range of adjustments in valve operation during actual engine running with minimum components and control mechanisms.
This invention is adapted to be embodied in a four-cycle engine having at least one poppet type valve supported for movement between an open and closed position for fluid interchange with a combustion chamber of the engine. A single rotating cam is associated with the valve. An actuating mechanism is interposed between the single rotating cam and the valve for operating the valve and for adjusting both the degree of lift and the lift curve of the valve so as to change the timing and lift operation of the valve.